This invention relates to a drive mechanism, and more particularly to a clutch-controlled drive mechanism well suitable for use with business machines such as electric or electronic typewriters or printers.
Power driven office machines such as, for example, electric typewriters, generally have a drive mechanism including an electric motor for cyclically driving a component of the machine. Such cyclically operable drive mechanisms typically include a constantly rotating drive shaft and a cycle clutch for operatively coupling the drive shaft to the machine component to drive the component in one direction for a cycle of operation. The electric motors used in such drive mechanisms have conventionally been AC motors which have a relatively large size but provide a relatively small torque output. AC motors are disadvantageously difficult to control appropriately so that they cannot be suitably employed for a drive mechanism of an electronic typewriter which has been very popular recently and requires a relatively or very precise control of machine components.
Stepping motors and servo motors are also very popularly used for drive mechanisms of office machines, due to their feasible and precise controllability. It is, however, disadvantageous in that they require such a high cost that they cannot be willingly incorporated in inexpensive popular business machines for office or personal use such as portable electronic typewriters.
Of late, small DC motors have exhibited a remarkable development and are very widely employed for drive mechanisms of business machines in accordance with individual applications. Small DC motors are advantageous in that they are inexpensive, easy to control and provide a relatively large output power or torque for their small size.
A portable electronic typewriter available on the market employs a small DC motor for its drive mechanism. Upon depression of a key of a typewriter keyboard, the DC motor is first energized and then a spring clutch is released to allow driving rotation of the motor to be transmitted to a member to be driven. After a cycle of rotation, i.e., a half rotation in the typewriter, of a driven element of the spring clutch, the clutch is rendered inoperative and then the motor is deenergized after a suitable interval of time. Thus, transmission of rotation is established sufficiently after the motor has reached its maximum speed, assuring the typewriter member to be driven satisfactorily by the motor. This arrangement, however, provides another problem that the motor produces disagreeable buzzing or even whizzing noises due to its rotation at a very high speed, sometimes up to about 6,000 rpm. These noises may cause an operator of the machine to be tired or irritated and may render her unwilling to use the machine.